Usually, a permanent magnet, brushless direct current (PM BLDC) motor includes a stator and a rotor. The rotor has a number of permanent magnet installed thereon. The stator includes a stator core with windings wound on the stator core. The windings generate a magnetic field which interacts with the permanent magnets to rotate the rotor. The rotor may have a structure shown in USA patent publication No. US2012-0181880A1 assigned to the same assignee. The rotor includes a number of rotor segments. Each rotor segment has a dovetail shaped end, which engages a dovetail shaped slot formed in a hub fixed to the shaft. However, it was found that the stress concentration on the edges of the dovetail shaped slots is relatively great, which may lead to malfunction of the rotor and failure of the motor.